1. Field of the Invention
The present invention relates to the allocation of resources on a transmission medium. The invention particularly but not exclusively relates to the allocation of resources for data on multiple media, and the protection of priority services when one or more of the multiple media fail.
2. Description of the Related Art
In data transmission systems data packets are transmitted on links. In many typical deployments data traffic is transmitted on multiple links, or one or more reserve links are provided to provide back-up to a main link in event of the main link failure.
Where one of multiple links fails, or when a main (or single) link fails, a mechanism must be provided to deal with the traffic allocated to the failed link.
In the event of one of multiple links failing, simply allocating the traffic from the failed link to one or more other links may not be satisfactory, since the one or more other links may not have the capacity to take their existing traffic in addition to the traffic from a failed link.
In addition, traffic is typically associated with a quality of service. Different data packets or data flows may be allocated to a particular traffic class, and that traffic class may be associated with a particular priority level. In addition to considering the allocation of the traffic volume amongst remaining available links or redundant links, it is also necessary to consider the priority of the traffic when all of the traffic will not fit on the available link space.
Simple proportional reduction of bandwidth for each type of traffic is unlikely to give desirable behaviour. For example, an application requiring 64 Kbps to work satisfactorily may break down completely when it is only given 32 Kbps, rather than working only half as well.
On any individual link, whether provided as a single link or one of a plurality of links, it may also be necessary to dynamically allocate traffic to the link as a result of changing conditions.
The changing conditions may be the presence or absence of different types of traffic. The changing conditions may be due to a change in capacity on a link. In any case where conditions change, the allocation of traffic to the link may need to be controlled to accommodate such changes.
It is an aim of the invention to provide an improved technique for allocating traffic to a link.